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United States Patent | 5,008,531 |
Ono ,   et al. | April 16, 1991 |
A light identifying system includes a photoelectric conversion unit for receiving a pulsed light from a light emitting part on a light receiving part to generate a light reception signal that varies in magnitude according to the quantity of the received light. A peak holding circuit has a time constant that is long compared with the pulse interval of the pulsed light. The peak holding circuit stores a peak value of the light reception signal for its time constant. The peak value is divided by a constant for application to a comparator. The comparator compares it with the light reception signal as a threshold. A peak value of the light reception signal is held, and the peak value thus held is specified as a threshold to the light reception signal, therefore in the unlikely event of decrease in the quantity of emitted light due to a secular change or of decrease in the quantity of received light due to mist and oil film, the threshold decreases accordingly.
Inventors: | Ono; Shoichi (Suwa, JP); Kobayashi; Atsuhito (Okaya, JP) |
Assignee: | Chinon Kabushiki Kaisha (Suwa, JP) |
Appl. No.: | 394067 |
Filed: | August 15, 1989 |
Current U.S. Class: | 250/222.1; 250/214R; 250/221 |
Intern'l Class: | G01V 009/04; H01J 040/14 |
Field of Search: | 250/222.1,214 B,214 SW,214 L,221,214 R 340/555,556,557 |
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4247767 | Jan., 1981 | O'Brien et al. | 250/221. |
4786800 | Nov., 1988 | Kamen | 250/222. |
4822996 | Apr., 1989 | Lind | 250/222. |
4829174 | May., 1989 | Booth et al. | 250/222. |
4851660 | Jul., 1989 | Juds et al. | 250/214. |
4851661 | Jul., 1989 | Everett, Jr. | 250/222. |
4851689 | Jul., 1989 | Hasegawa | 250/214. |
Foreign Patent Documents | |||
0202601 | Nov., 1986 | EP. |